When we hear a sound we can often determine where the sound is coming from. This is called localization. The process of placing a sound in a sound field (space) is called spatialization. In the production of audio programs, most modern mixers have a 2-channel mixed output where one speaker is positioned to the left of the listener and the other is positioned to the right, i.e., a stereophonic configuration. Another configuration is quadraphonic, in which there are four speakers surrounding the listener in a rectangular configuration, i.e., left front, left rear, right front, right rear. As used herein, the term “quadraphonic” generally represents any number of channels more than 2 (stereophonic).
For spatialization, early mixers offered simple signal routing switches where the user could manually select which speaker(s) the signal would be present in. Subsequent developments resulted in the ability to move a sound smoothly within the spatial sound field (between speakers), which is called panning. In a typical stereo mixer, panning is accomplished with a single-axis rotary potentiometer. For quadraphonic mixing, panning has been accomplished with: (1) a set of 4 potentiometers where each potentiometer corresponds to one of 4 speakers and controls the level of a channel in each speaker; (2) a two-axis X/Y controller such as a joystick or touchscreen where the position of a single point on a grid defines the location of the sound; or (3) a combination of two rotary controls, one for controlling front/back movement of the sound and the other for controlling left/right.
Due to size and expense, quadraphonic mixing hardware was considered bulky and inefficient for pan control of more than one channel, and prior art mixers were thus limited to only one panner per mixer. The result is that only one channel can be panned at a time with conventional quadrophonic mixing hardware, making real-time panning of more than one sound impossible and requiring productions with animated panning of more than one sound to need regular reconfiguration of the system. Therefore, most quadraphonic mixing is accomplished with software on a computer, though still with two-axis pan controls. Automating two-axis pan controls requires two channels of automation, one for each axis, and are thus more difficult and complicated to use.